Field of the Invention
The present invention relates to a developing device using a two-component developer and an image forming apparatus using the developing device. More specifically, the present invention relates to a developing device and an image forming apparatus using the same which are configured to cope with an increase in a charge amount of toner in use.
Related Art
Conventionally, image forming apparatuses using toner as a color former have been used. In the toner-type image forming apparatuses, when image forming is to be performed, the toner is agitated (stirred) to be frictionally charged, and the charged toner is transferred from a developing roller onto a photoconductor by a developing bias so that a latent image on the photoconductor is developed to be formed as a visible image. In an image forming apparatus having the above configuration, a charge amount of the stored toner tends to increase when image forming jobs are frequently performed and the amount tends to decrease during non-image forming period.
Among the toner-type image forming apparatuses, especially, a conventional example in which toner and carrier are used as a two-component developer has been described in Patent Document 1. An image forming apparatus described in the document adopts a conductive agitating member for agitating a developer. Further, it is described in the document that a bias is applied between a developing roller (a developing sleeve in the document) and the agitating member. Thus, the apparatus in Patent Document 1 is targeted to efficiently remove electric charge of the carrier and prevent charge failure in the toner.